Among individuals with the serologically defined HLA-DR7 specificity, six distinct mixed lymphocyte culture (MLC)-defined HLA-D specificities have been described: Dw7, Dw11, Dw17, DW7L, Dw11S, and Dw blank. The family of DR7-associated HLA-D specificities will be used as a system in which to address the long-term objectives of better defining the structure-function relationships of human Ia molecules and the basis for polymorphism generation among Ia molecules. 1. We will determine the structural differences or similarities among Ia genes and the corresponding proteins from cells representing the six DR7-associated HLA-D specificities by constructing cDNA libraries from these cells in the Okayama and Berg expression vector and determining the nucleotide sequences of cDNA clones corresponding to the DR, DQ, and DP alpha and beta chains. 2. We will define the molecular basis for the finding in studies at the protein level that Dw11 homozygous cells express only one DR beta chain by: a) approximating the number of Dw11 DR beta genes using Southern blot analysis, b) analyzing Dw11 DR beta mRNA to determine if an RNA abnormality prevents expression of the DR beta 2 chain, and c) sequencing DR beta genes from a Dw11 genomic library to determine which DR beta gene has been deleted or to identify and characterize the defective gene. 3. We will use DNA-mediated gene transfer of Ia alpha and beta chain cDNAs in the Okayama and Berg expression vector to determine which hybrid DQ molecules and hybrids DP molecules occur and whether mixed-isotype molecules occur in man. The findings of these studies will contribute to the understanding of the diversity of human Ia molecules and the function of immune response genes, which may play important roles in the determination of human health and disease.